Dale Earnhardt Jr. met with renowned concussion specialists at the University of Pittsburgh Medical Center's sports medicine concussion program Tuesday.

Earnhardt was not given medical clearance to participate in this past Saturday's Sprint Cup race at Charlotte Motor Speedway or this week's race at Kansas after suffering multiple concussions over the past six weeks.

He was accompanied to Pittsburgh by NASCAR primary physician Dr. Jerry Petty as a part of the original rehabilitation plan that was put in place last week.

Earnhardt met with Dr. Michael Collins, the executive director of the concussion program that helped developed the ImPACT baseline test used in the IndyCar series and other contact sports.

NASCAR officials are reviewing with their medical team all aspects of issues involving concussions, including baseline testing that IndyCar uses as part of its preseason testing.

The baseline test taken before an injury gives doctors an idea of what functions may have suffered from a head injury. The test in post-injury care helps experts manage the injury more accurately.

Earnhardt first suffered a concussion in an Aug. 29 test at Kansas Speedway in which the impact registered 40 G-forces. He suffered symptoms of a headache again after an Oct. 7 crash on the last lap at Talladega Superspeedway.

Earnhardt visited Dr. Petty following the Talladega crash. After several tests, Dr. Petty opted to sit NASCAR's most popular driver for at least two races.

During his visit to Pittsburgh, Earnhardt stopped by the Pittsburgh Steelers' practice facility, and a photo of him shaking hands with coach Mike Tomlin was later posted on Twitter.